1. In a medium skillet, warm the oil over medium heat. Add the onion and saute, stirring occasionally, until light golden, about 8 minutes.
2. Add the garlic and saute for 1 minute. Add the tomatoes, oregano, and pepper. Reduce the heat to medium-low and simmer until the sauce is thickened, about 15 minutes.
3. Meanwhile, preheat the oven to 450°.
4. Add the olives and capers to the sauce, and simmer for 5 minutes to blend the flavors. Remove the pan from the heat.
5. Coat the baking dish with a spoonful of the sauce. Place a fillet in the dish and top with a spoonful of the sauce. Overlap with a second fillet and top with sauce. Add the remaining fish and sauce in the same manner.
6. Pour the wine over the fish and bake for 6 to 8 minutes, or until the fish just flakes when tested with a fork.
7. Transfer the fish to a platter. Strain the pan juices into a small saucepan. Cook over high heat until slightly thickened, 2 to 3 minutes. Pour the reduced pan juices over the fillets and serve.